The invention relates to a steplessly blockable device comprising a cylinder with a cylinder axis, a cavity, a cylinder inner surface and two end walls, a piston rod conducted in sealing manner through at least one of the end walls and movable in the direction of the cylinder axis in relation to the cylinder, a piston unit connected within the cylinder with the piston rod, which unit rests in sealing manner on the cylinder inner surface and divides the cavity within the cylinder into two working chambers, a fluid filling in the working chambers, a by-pass connection connecting the two working chambers with one another, and a shut-off valve arrangement, actuatable from the exterior of the cylinder, in the by-pass connection.
Such setting devices are used for example for setting doors or flaps into desired open positions. In order to effect the setting, the shut-off valve is opened. When the desired setting is reached, the shut-off valve is closed again so that then the door or flap is made fast. It can occur that a closing or opening force is exerted upon the door or flap without the shut-off valve being opened. Then extremely high forces occur on the setting device and on the mounting of the door or flap. In that case deformations can easily occur to the setting device and/or to the mounting of the door or flap. Under some circumstances the piston rod can be torn violently out of the piston.